A digital still camera or digital video camera on which the image pickup device using the solid image pickup element such as the CCD type image sensor or CMOS type image sensor is mounted, is developed. Further, because the image pickup device using these solid image pickup elements is appropriate for the down-sizing, recently, they are also mounted on small sized information terminals including a movile phone. Following a further down sizing and high pixelation of the solid image pickup element, the requirement for the down sizing and for making the high performance also in image pickup lenses mounted on these image pickup devices is increasing.
As an image pickup lens for such a purpose, because the higher performance can be obtained comparing to the lens of 2-lens composition or 3-lens composition, the lens of 4-group 4-lens composition includes, in order from the object side, an aperture stop, the first lens having a positive refractive power, the second lens having a negative refractive power, the third lens having a positive refractive power, and the fourth lens having a positive or negative refractive power, is well known. Among them, particularly a lens having a short lens-total length (a distance on the optical axis from the aperture stop to the image side focal point) is disclosed, for example, in Patent Document 1.
(Patent Document 1) Tokkai No. 2002-365529
Hereupon, the image pickup lens of a type written in Patent Document 1 has a so-called telephoto type power arrangement in which the first lens is a positive lens, the second lens is a negative lens, the third lens is a positive lens, and the fourth lens is a negative lens, and is a type in which a size reduction of the image pickup lens is tried thereby. However, on the one hand, in the image pickup lens of the Patent Document 1, there are defects in which the aberration correction is insufficient for the correspondence to the high pixelation of the solid image pickup element, or the wide angle-formation of the photographic image angle.
In view of such problems, the present invention is made, and an object of the present invention is to provide an image pickup lens of 4-group 4-lens composition which is small sized, and by which the higher image formation performance can be obtained, and which is appropriate for the wide angle-formation, and has a good image side telecentricity, and an image pickup device using it.
The image pickup lens according to the present invention includes, in order from the object side, a lens having a positive refractive power (hereinafter, a positive lens), a lens having a negative refractive power (hereinafter, a negative lens), a positive lens, and a lens at least whose one surface is an aspheric surface shape. This composition is a power arrangement called a so-called triplet, and when designed so as to satisfy a predetermined condition, the spherical aberration, coma, and chromatic aberration in these lenses can be appropriately corrected. Further, when the forth lens of an aspheric surface shape is arranged, the aberrations out of axis including the distortion aberration can be corrected, and further a good image side telecentricity can be obtained.